ASHRAE+62.1-2022+(1) - Page 066
Extracted Content
(This appendix is not part of this standard. It is merely informative and does not contain require- ments necessary for conformance to the standard. It has not been processed according to the ANSI requirements for a standard and may contain material that has not been subject to public review or a consensus process. Unresolved objectors on informative material are not offered the right to appeal at ASHRAE or ANSI.)
INFORMATIVE APPENDIX K INFORMATION ON NATURAL VENTILATION
K1. OUTDOOR AIR QUALITY DATA
Outdoor air quality data may be considered valid if it is demonstrated that the data are both physically and spatially representative.
Physically representative data accurately reflect the air quality conditions at the monitoring station from which they are derived. Data are considered physically representative if they are obtained from
a. reports of historical levels of air pollutants published by the relevant local, regional, or federal entity
with statutory responsibility for collecting and reporting air quality information in accordance with applicable air quality regulations, or b. an on-site monitoring campaign that is verifiably comparable to local, regional, or federal guidelines and
methods for demonstration of compliance with applicable air quality regulations.
Spatially representative data are collected from a monitoring site that may differ from the proposed project location but is informative of the air quality conditions at the proposed project location. Data may be considered spatially representative if they are
a. the same as those used by the entity charged with demonstrating regulatory compliance for the geo graphic region that includes the proposed project location, or b. derived from an on-site monitoring campaign that also meets the requirement stated by criteria (b)
above.
K2. NATURAL VENTILATION RATE
When calculating the ventilation rate, specific path(s) of the intended airflow passage must first be determined along with flow directions. The two driving forces for natural ventilation are buoyancy and wind, which can work cooperatively or competitively based on the environmental conditions of wind speed, direction, indoor/outdoor air/surface temperatures, as well as the intentional airflow path and mechanisms.
a. In the case of an engineered natural ventilation system that results in multiple flow scenarios, each force
must be examined and considered separately. b. Specific pressure-based calculation of natural ventilation flow rate is documented in ASHRAE Hand-
book—Fundamentals, Chapter 16, Section 10:
- Buoyancy-induced airflow can be calculated following Equation 46.
- Wind-driven airflow can be calculated following Equation 45.
- The overall pressure (driven by both wind and stack effect) converted to resulting pressure difference between openings can found in Equation 44.
For obtaining wind-driven pressure, several methods are available:
a. ASHRAE Handbook—Fundamentals, Chapter 24, provides a method to convert wind speed and direction
into pressure coefficients that can be used to determine wind-driven pressure. b. CIBSE AM10, Chapter 4, provides a method to account for wind-driven ventilation and outlines specific
challenges to it in Section 4.4.1. c. If the building has undergone wind tunnel test for structural stress, the same test can provide detailed
pressure coefficients. d. Outdoor airflow simulation (such as computational-fluid-dynamics-based simulation) can be used to
obtain the specific flow condition at the intended openings.
For intended openings that are large, such as an open atrium or open balcony, and/or when the flow path is not well defined, such as when only single or single-side openings are available, the pressure-based method can be invalid, and outdoor-indoor linked simulation should be used.
64 ANSI/ASHRAE Standard 62.1-2022